Alzheimer's disease (AD) and multi-infarct dementia (MID) are the two leading causes of progressive and irreversible dementia. Identifying risk factors associated with AD and MID is an important step in the search for etiology as well as intervention and prevention strategies. The major objective of this research application is to identify and clarify risk factors for AD and MID in an urban black aged population. Blacks have been underrepresented in biomedical, behavioral and psychosocial studies of dementia. The investigators propose to study epidemiological, medical, neuropsychological and neuroradiological characteristics by carrying out a case-control study in two groups of index cases, blacks with AD and blacks with MID, and a control group composed of blacks with multiple cerebral infarcts but without cognitive impairment. The second major objective of this project is to follow the case-control populations longitudinally to determine the rate of decline in cognitive status, to determine and compare outcome variables measuring cognitive and functional status, and mortality among black AD and MID cases with respect to descriptive history of these variables over time, and to develop hypotheses about medical and psychosocial factors that contribute to the survival disadvantage of aging black Americans. A third major objective is to accumulate enough standardized neuropathological observations on deceased cases using neuropathological criteria developed by CERAD to validate clinical diagnoses of AD and clarify valid criteria for MID in blacks. The investigators are proposing a case-control study to gather empirical data on risk factors as a prelude to the design of targeted intervention studies.